Modern inventory systems, such as those in mail order warehouses, supply chain distribution centers, airport luggage systems, and custom-order manufacturing facilities, face significant challenges in responding to requests for inventory items. As inventory systems grow, the challenges of simultaneously completing a large number of packing, storing, and other inventory-related tasks become non-trivial. In inventory systems tasked with responding to large numbers of diverse inventory requests often need to balance competing needs and requirements. For instance, less frequently access inventory items are sometimes stored in a densely-packed storage area to save space. However, moving inventory items out of or into such densely-packed storage areas can be inefficient using existing ground-based drive units.